Cytokines and growth factors play critical roles in normal homeostasis of immune functions. TGF-?1 is the dominant regulator of inflammatory responses. We have earlier generated TGF-?1-/- mice that exhibit multifocal inflammation associated with increased adhesion of leukocytes to endothelium, aberrant expression of MHC class-I and -II antigens, and autoimmune manifestations similar to Sjogren syndrome. Moreover, depletion of CD8 cells ameliorated health status of TGF-?1 null mice. To delineate role of TGF-?1 in aberrant MHC expression, TGF-?1 null mice were generated in the MHC-I and MHC-II deficient backgrounds. TGF-?1 X MHC-I null mice exhibit increased longevity associated with reduced inflammation, diminished autoimmune manifestations and significantly elevated myelopoiesis. Although the TGF-?1 X MHC-II mice exhibited lack of inflammation and autoimmune response, they showed neonatal mortality associated with increased myelopoiesis and metaplasia. These results indicate a dominant role of TGF-?1 in leukocyte maturation and function. To assess the therapeutic potential of circulating levels of active TGF-?1, we generated mice with endocrine expression of active TGF-?1 on a TGF-?1 null background (TGF-?1(-/-/TG)) by crossing TGF-?1(+/-) mice with transgenic mice (TG) that express recombinant TGF-?1 specifically in the liver and secrete it in the blood. The TGF-_1(-/-/TG) mice exhibit a survival profile similar to the TGF-?1 (-/-) mice indicating a failure to rescue the lethal phenotype. However, serum TGF-?1 levels in theTGF-?1 (-/-/TG) mice were restored to normal levels with expression in all the tissues notably in the kidney and spleen. Histopathology showed reduced inflammation in all target tissues, especially in the heart. Interestingly unlike TGF-? (-/-) mice, the TGF-?1(-/-/TG) mice have glomerulonephritis in their kidneys similar to the TG mice. Thus, the phenotype of TGF-?1 (-/-/TG) animal model indicates the potential role of circulating active-TGF-_1 in reducing inflammation, but its failure to rescue lethality in TGF-_1 null mice indicates a critical role of autocrine TGF-?1.